1. Field of the Invention
The invention relates to a gas-discharge display device constructed of:
(a) a vacuum-tight envelope with two mutually parallel wall plates (front plate, back plate) which are disposed one behind the other in the direction of view, is filled with a gas; PA0 (b) a control unit which is located in the envelope and is regularly perforated, divides the interior of the envelope into a back and a front space (gas discharge space and post-acceleration space, respectively); PA0 (c) at least one cathode (plasma cathode) and at least one anode (plasma anode) is in the gas discharge space; PA0 (d) the front plate carries on its backside a cathodoluminescent layer and a layer electrode (post-acceleration anode); PA0 (e) the control unit contains at least one electrode plane extending parallel to the wall plates, with at least one conductor; PA0 (f) the post-acceleration cathode is coated with an implantation protection layer of a high-melting metal. PA0 (a) a gas-filled space gas-tightly closed on one side by a front plate and on a side opposite thereto by a back plate parallel to the front plate, the plates disposed one behind the other; PA0 (b) a control unit dividing the gas-filled space into a back space as a gas discharge space and a front space as a post-acceleration space, the control unit having regularly spaced perforations; PA0 (c) at least one plasma cathode and at least one plasma anode in the gas discharge space wherein a gas discharge burns between the plasma electrodes in operation; PA0 (d) the front plate carrying on its backside a cathodoluminescent layer and a layer electrode as a post-acceleration anode; PA0 (e) the control unit having at least one electrode plane extending parallel to the wall plates with at least one conductor as a post-acceleration cathode; PA0 (f) means for applying a high voltage larger than 1 kV between the post-acceleration anode and the post-acceleration cathode of the foremost electrode plane, and with a small distance between both post-acceleration electrodes to suppress igniting the gas discharge in the post-acceleration space; the combination therewith of PA0 (g) a coating on the post-acceleration cathode of a protective implantation layer of a high-melting metal from the subgroups A of the fourth to eighth group and of the fifth to sixth period of the periodic system of the elements.
2. Description of the Prior Art
A gas discharge display device (plasma panel) is disclosed in U.S. application Ser. No. 470,702 filed Feb. 28, 1983, based on German Application No. P 3207685.
In the flat picture screen of the mentioned application, electrons of a gas discharge are sent through selectively opened holes of a control unit into a space free of plasma in which they take on energies of several kV and finally generate light dots on a luminescent screen.
With the concept of separate electron generation and acceleration, it is possible to display colored video pictures with an acceptable quality. However, maintaining all the important operating parameters stable over extended operating periods has not been successful to date. Thus, a particular parameter is the operating voltage of the plasma which increases regularly and if the picture screen is switched to bright continuously, can assume twice the value after a few hundred operating hours. Such a voltage drift poses enormous requirements with respect to the driving circuit and the cathode and should be avoided at all costs.
German Published Non-Prosecuted Application No. DE-OS 29 29 270 (U.S. Pat. No. 4,329,626) discusses filling the display device with H.sub.2, using an aluminum cathode and keeping the cathode surface under a thin oxide layer during the gas discharge. Practice has shown, however, that these measures are not sufficient especially in cases in which the display device is continuously operating for an extended period of time. There is no substantial improvement even if other gases or cover layers are used, as for instance an Ne-Ar mixture and an MgO/Al.sub.2 O.sub.3 --Ta/Mo skin (IBM Technical Disclosure Bulletin 25 (1983), Page 658).